Gaskets are commonly used to assist in the shielding of electrical components from electromagnetic radiation (EMR). This shielding is extremely important to eliminate cross-talk and spurious signals that would occur when electrical components are densely packed together or when the electrical components are subject to impinging EMR. In a typical case, the electrical components are placed in a metallic receptacle and a metallic cover which has a conductive gasket attached to it by an adhesive layer is fastened to the receptacle. The gasket is generally made conductive by the inclusion of metallic micro-particles in an elastomer during fabrication of the gasket.
These gaskets have, however, proved less than satisfactory for good EMR shielding and thermal conductivity. This was due basically to the fact that the adhesive used to bond the gasket to the cover is a poor electrical conductor, and a poor thermal conductor due to its erratic application, and thus the electromagnetic radiation is able to pass between the gasket and the cover and enter the receptacle, while heat transfer is impeded. In addition, in the case of metallic-coated glass microballoons, since the microballoons are free to move in the elastomer under vibration, the microballoons lose contact with one another and increase the resistivity of the gasket, thereby resulting in decreased resistance to EMR. Furthermore, the use of adhesives causes uncontrolled variations in gasket conductance and height, due to the inability to apply them in a perfectly uniform thickness. This results in improper closure both where the gasket height is too low and where the gasket height is too high due to insufficient local closure force to properly deflect the gasket. Moreover, since the gaskets are generally cut after curing to fit a particular cover shape or contour, the micro-particles are exposed to air and proceed to corrode, resulting in a general degradation of the properties of the gasket. Such gaskets also degrade in their electrical properties due to handling, stretching and elongation, due to the failure of the adhesives over time, and due to handling, shelf-life and pot-life (during application) adhesive complications. Typical gaskets, their method of manufacture, and the manufacture of the metallic micro-particles are described in U.S. Pat. Nos. 3,140,342, 3,194,860, and 3,202,488, respectively. Finally, existing gaskets cannot be used as shields against ultrahigh frequencies (&gt;20 GHZ) and for micro-integrated circuits where complicated gasket designs and tight tolerances are essential.
Accordingly, it is a general object of the present invention to provide an improved shielding gasket for use against electromagnetic radiation.
It is another object of the present invention to provide a shielding gasket that is integrally bonded to a surface for use against electromagnetic radiation and which also provides good thermal conductivity.
It is a further object of the present invention to provide an improved method of making a shielding gasket-surface combination that effectively shields against electromagnetic radiation, while providing effective thermal conductivity.
It is still another object of the present invention to provide a shielding gasket whose resistivity is stable under conditions of vibration.
It is still a further object of the present invention to provide a shielding gasket which will not degrade in its properties during application and use.